1. Field of the Invention
This invention relates generally to a digital programmable latch for storing a logical "0" or a logical "1" and, more particularly, to a digital programmable latch for storing a logical "0" or a logical "1" that allows volatile temporary writes to be stored in the latch prior to the latch being permanently programmed.
2. Discussion of the Related Art
Many module systems require customization of system components at the time that the components are assembled as part of a module assembly or module installation. For example, for many module sensor systems, the normal parametric spreads of sensor elements in the system prevents a one-size-fits-all solution to the signal conditioning of the sensor output. Minor differences in sensor element gain, offset, resonant modes, temperature characteristics, etc. make it necessary to trim or customize the signal conditioning to a specific sensor element at the time of assembly. Examples of things that need to be independently calibrated include reference voltage level inputs to a comparator, identification codes, etc. Once this customization has been performed, it will remain as part of the sensor element throughout the life of the product.
Generally, arriving at the proper customization for a particular sensor element is an iterative process. Therefore, a need exists for a technique to iteratively determine the proper compensation for a given sensor element, and then, to permanently program the signal conditioning device with these values.
Known methods of compensating the output of sensor elements have included use of laser trimming of resistors on a module substrate or the use of a "zener zapping" technique. With the zener zapping technique, an array of zener diodes is used to trim in a value by selectively shorting out (zapping) the junctions of diodes that are in parallel with certain resistors. This process effectively removes the resistor from the circuit. However, a number of drawbacks exist with this technique. For example, large resistor values are required due to the relatively high resistance of the shorted junction, the large size of the circuitry required to address and short out a particular diode, and the relatively high current levels required to short out the diode junctions.
What is needed is a technique for determining proper compensation for a customized component prior to permanent programming, that does not suffer the drawbacks of the prior art techniques. In other words, what is needed is a bit storage circuit that allows multiple temporary programming before being permanently programmed. It is therefore an object of the present invention to provide such a technique.